package org.bouncycastle.asn1.x509;

import java.util.Enumeration;

import org.bouncycastle.asn1.ASN1Encodable;
import org.bouncycastle.asn1.ASN1EncodableVector;
import org.bouncycastle.asn1.ASN1Sequence;
import org.bouncycastle.asn1.ASN1TaggedObject;
import org.bouncycastle.asn1.DERObject;
import org.bouncycastle.asn1.DERSequence;
import org.bouncycastle.asn1.DERTaggedObject;

/**
 * This class helps to support crossCerfificatePairs in a LDAP directory according RFC 2587
 * 
 * <pre>
 *     crossCertificatePairATTRIBUTE::={
 *       WITH SYNTAX   CertificatePair
 *       EQUALITY MATCHING RULE certificatePairExactMatch
 *       ID joint-iso-ccitt(2) ds(5) attributeType(4) crossCertificatePair(40)}
 * </pre>
 * 
 * <blockquote> The forward elements of the crossCertificatePair attribute of a CA's directory entry shall be used to store all, except self-issued
 * certificates issued to this CA. Optionally, the reverse elements of the crossCertificatePair attribute, of a CA's directory entry may contain a
 * subset of certificates issued by this CA to other CAs. When both the forward and the reverse elements are present in a single attribute value,
 * issuer name in one certificate shall match the subject name in the other and vice versa, and the subject public key in one certificate shall be
 * capable of verifying the digital signature on the other certificate and vice versa.
 * 
 * When a reverse element is present, the forward element value and the reverse element value need not be stored in the same attribute value; in other
 * words, they can be stored in either a single attribute value or two attribute values. </blockquote>
 * 
 * <pre>
 *       CertificatePair ::= SEQUENCE {
 *         forward        [0]    Certificate OPTIONAL,
 *         reverse        [1]    Certificate OPTIONAL,
 *         -- at least one of the pair shall be present -- }
 * </pre>
 */
public class CertificatePair extends ASN1Encodable {
    private X509CertificateStructure forward;

    private X509CertificateStructure reverse;

    public static CertificatePair getInstance(Object obj) {
        if (obj == null || obj instanceof CertificatePair) {
            return (CertificatePair) obj;
        }

        if (obj instanceof ASN1Sequence) {
            return new CertificatePair((ASN1Sequence) obj);
        }

        throw new IllegalArgumentException("illegal object in getInstance: " + obj.getClass().getName());
    }

    /**
     * Constructor from ASN1Sequence.
     * <p/>
     * The sequence is of type CertificatePair:
     * <p/>
     * 
     * <pre>
     *       CertificatePair ::= SEQUENCE {
     *         forward        [0]    Certificate OPTIONAL,
     *         reverse        [1]    Certificate OPTIONAL,
     *         -- at least one of the pair shall be present -- }
     * </pre>
     * 
     * @param seq
     *            The ASN.1 sequence.
     */
    private CertificatePair(ASN1Sequence seq) {
        if (seq.size() != 1 && seq.size() != 2) {
            throw new IllegalArgumentException("Bad sequence size: " + seq.size());
        }

        Enumeration e = seq.getObjects();

        while (e.hasMoreElements()) {
            ASN1TaggedObject o = ASN1TaggedObject.getInstance(e.nextElement());
            if (o.getTagNo() == 0) {
                forward = X509CertificateStructure.getInstance(o, true);
            } else if (o.getTagNo() == 1) {
                reverse = X509CertificateStructure.getInstance(o, true);
            } else {
                throw new IllegalArgumentException("Bad tag number: " + o.getTagNo());
            }
        }
    }

    /**
     * Constructor from a given details.
     * 
     * @param forward
     *            Certificates issued to this CA.
     * @param reverse
     *            Certificates issued by this CA to other CAs.
     */
    public CertificatePair(X509CertificateStructure forward, X509CertificateStructure reverse) {
        this.forward = forward;
        this.reverse = reverse;
    }

    /**
     * Produce an object suitable for an ASN1OutputStream.
     * <p/>
     * Returns:
     * <p/>
     * 
     * <pre>
     *       CertificatePair ::= SEQUENCE {
     *         forward        [0]    Certificate OPTIONAL,
     *         reverse        [1]    Certificate OPTIONAL,
     *         -- at least one of the pair shall be present -- }
     * </pre>
     * 
     * @return a DERObject
     */
    public DERObject toASN1Object() {
        ASN1EncodableVector vec = new ASN1EncodableVector();

        if (forward != null) {
            vec.add(new DERTaggedObject(0, forward));
        }
        if (reverse != null) {
            vec.add(new DERTaggedObject(1, reverse));
        }

        return new DERSequence(vec);
    }

    /**
     * @return Returns the forward.
     */
    public X509CertificateStructure getForward() {
        return forward;
    }

    /**
     * @return Returns the reverse.
     */
    public X509CertificateStructure getReverse() {
        return reverse;
    }
}
